In a deal that unites two of the nation's largest solar companies, Sunrun and Sungevity have formed an alliance to sign up at least 10,000 new residential customers through 2016.

Both companies offer solar panels to homeowners for little or no money down, with customers paying month by month. Under the new agreement, Oakland's Sungevity will recruit customers, while Sunrun, based in San Francisco, will provide financing and own the arrays. The companies hope to install enough solar arrays to generate 70 megawatts of electricity.

The deal is not exclusive. Sungevity will continue to work with other financing partners, while Sunrun will pursue customers through alternative channels.

Both companies cast the deal as playing to their core talents. Known for customer service and acquisition, Sungevity was the first solar company to offer price quotes online within 24 hours.

"Ultimately, as this industry goes mainstream, it's going to be about customer service, and that's where our strengths lie," said Sungevity CEO Andrew Birch.

The alliance comes amid Sunrun's efforts to expand its operations and challenge SolarCity, the country's dominant solar leasing company. Founded in 2007, Sunrun pioneered the concept of offering solar power as a service to homeowners who wanted panels but couldn't afford them. Sunrun typically finances and owns the arrays while hiring other businesses to install the equipment.

But in recent years, SolarCity, the fast-growing San Mateo business chaired by Elon Musk of Tesla Motors, has overtaken Sunrun. SolarCity now accounts for one third of all new residential solar arrays in the country, typically handling both financing and installation.

So Sunrun is bulking up. In February, the company bought the residential operations of REC Solar as well as SnapNRack, which makes panel-mounting systems that reduce installation times. Those deals, both for undisclosed sums, will help Sunrun become more of a full-service provider - like SolarCity.

The Sungevity agreement provides Sunrun a big pipeline of projects. But Jurich of Sunrun said the alliance also shows that Sunrun won't abandon its original approach of working through partners.

"We're confident this is the winning model," she said. "You can't just be good at selling direct to the consumer. You have to meet them where they want to purchase."